Customer would like to migrate CLB to NLB/ALB.

A customer would like to migrate CLB to NLB/ALB. (This customer used the persistent connection to EC2 instances so that they are very sensitive to dis- and re-connection of it at bulk size.)

Do we have any recommendation steps or best practice for this?

I just found that below link and pdf file which described You can shift traffic all at once or you can do a weighted distribution under "Update DNS Routing with Amazon Route 53." However this is not enough for guiding or instructing them to do.

Blue/Green Deployments on AWS.pdf (https://d1.awsstatic.com/whitepapers/AWS_Blue_Green_Deployments.pdf)